Multiple sclerosis (MS) is a neurodegenerative disease that invariably leads to difficulties with walking. Neuromuscular electrical stimulation (NMES) can be an effective intervention for a range of conditions that reduce motor function. Wide pulses (0.5-1 ms) activate a greater proportion of sensory axons and thereby augment the central contribution to evoked contractions, whereas narrower pulses (0.2-0.4 ms) preferentially activate motor axons. The differential activation of motor and sensory axons is attributable to the longer strength-duration time constant and lower rheobase of sensory axons.
PURPOSE: To compare the influence of pulse width on the changes in motor function elicited by a 6-wk NMES intervention in individuals diagnosed with MS. We hypothesized that the improvements in motor function would be greater for participants who received wide-pulse NMES.
METHODS: Eleven persons (51.4 ± 6.7 yrs, 5 women) with clinically diagnosed MS participated in a 6-wk NMES intervention. The average score on the first page of the Patient Determined Disease Steps questionnaire was 3.4 ± 1.5. Intervention sessions entailed 10 min of stimulation of the calf muscle and 10 minutes of stimulation of the tibialis anterior muscle. Performance evaluation included a 6-min walk test, a 25-foot walking test, and strength tests of the dorsiflexor and plantarflexor muscles for both limbs. The 6-min walk test provides a measure of walking endurance, whereas the 25-ft walking test indicates fast walking speed. Evaluation sessions were performed at week 0, week 6 (after the 6 wks of treatment), and week 10 (4 wks after intervention).
RESULTS: While not yet sufficiently powered to compare the narrow- and wide-pulse groups, the data were collapsed across groups and pairwise comparisons suggested that walking endurance was significantly improved (437 ± 137 m to 464 ± 162 m, P = 0.027) after the intervention (week 6). In contrast, there was no statistically significant change in fast gait speed (5 ± 11 m/s to 4 ± 8 m/s, P = 0.6). Improvements in walking endurance lasted through the retention session (week 0: 453 ± 133 m; week 10: 490 ± 140 m, P<0.01).
CONCLUSION: A 6-wk treatment with NMES can improve walking endurance, but not fast walking speed, in persons with MS who self-report walking limitations.
Supported by NIH under award number R03HD079508.